Just remember that you’ll need to uninstall any previous versions of XP SP3 before proceeding with the newest Release Candidate. Similarly you’ll need to uninstall RC2 before you’ll be able to install the final version whenever Microsoft decides to release it. It’s a hassle, I know, but this is a good cure if you’re starting to get a nervous twitch from not running enough pre-release software. It happens to the best of us.